Topic: Determining whether a muffler will work with 4-1/'78 CB750

[Kev Nemo]

So I want this:http://www.jcwhitney.com/autoparts/ItemBrowse/c-10111/s-10101/p-100000142715/mediaCode-ZX/appId-100000142715/Pr-p_CATENTRY_ID:100000142715

but I'm worried it won't work with my 4-1 on my CB750. I have no idea what kind of 4-1 I'm running and I'm having problems figuring out the pipe diameter. I always thought you wrapped the tape around, and then divided by 2; my neighbor said you hold the tape next to the pipe and measure that way. If I wrapped the pipe, it's about 8 inches around or 4inches standard diameter. Seems really big.

Any ideas?

[KingCustomCycles.com]

I am fairly certain the mufflers are sold by inlet diameter like 1 7/8" or 2 1/4 inch etc.  Most aftermarket mufflers come with a package of spacers to size them down.  In order to size them up, have a local muffler shop make you an adapter on their pipe expansion tool.  My shop does it for free from the scrap bin.   

[Kev Nemo]

Ok so here's the info:"Includes clamp and 3 collars to fit over 1-3/8", 1-1/2", 1-5/8" or 1-3/4" outside diameter pipes. Approx. sizes: 18"L flares to 3-3/4" diam., then tapers down to 1-3/4". So if it goes to 1-3/4 (the biggest) and it's smaller than my pipe from the collector back, will that be way too much backpressure?

Pics for reference:



if you could identify them it would great!

[bobrhix]

kev,,, chev looks kool!!   bike 2

[Tower]

Those look like Mac pipes or Mac knockoffs (the squarish bends are a giveaway) with a non-Mac motorcycle muffler,

The relationship between circumference (c) and diameter (d)  is:
  d = c / 3.1416
e.g. 8" circumference = 2 1/2" diameter

b.t.w. 2 1/2" collector is about as standard as you can get.

If putting in a muffler with less than 2 1/2" pipe there will be added back pressure - but that's not necessarily a problem.  The golden "rule-of-thumb" is about 90% reduction i.e 2 1/4" pipe.  Further reduction could be problematic.

[Kev Nemo]

kev,,, chev looks kool!!   bike 2

It's for sale if your interested!

So would 1-3/4 be too much of a reduction from 2-1/2?

[78CB750CAFE]

2 1/2 pipes into a 2 1/4  free flowing muffler is what I run and it runs and sounds great. I paid way too much to get a flange/adapter welded up at a local muffler joint, but there are easier answers if your muffler is a slip on, or has a collar for attachment. Most auto shops have cheap pre made reducers for exhaust pipes if your mufflers adapters dont work well.

[Kev Nemo]

Yeah, if 2 1/4 is the smallest, then that muffler won't work. Damn-any idea where I can find one that style but in a 2 1/4? I guess I could cut it, but that seems more trouble than it's worth.

[goon 1492]

2 1/2 pipes into a 2 1/4  free flowing muffler is what I run and it runs and sounds great. I paid way too much to get a flange/adapter welded up at a local muffler joint, but there are easier answers if your muffler is a slip on, or has a collar for attachment. Most auto shops have cheap pre made reducers for exhaust pipes if your mufflers adapters dont work well.

Um...Yeah I'm pretty sure we are gonna need more pics please and a full report on that beast would render a big fat thankyou from the goon is that a two brothers racing pipe ya got there, what did the pipe spec out for originally.

[Kev Nemo]

So I'm thinking I could get the shorty muffler, go up an inch on it, and cut. I'm not concerned about marring the chrome since I'm going black with it anyway.

thoughts and opinions?

[Tower]

You would need to weld a flange or connector piece to the cut in order to clamp it to the collector.

[Kev Nemo]

You would need to weld a flange or connector piece to the cut in order to clamp it to the collector.

Hmm-my muffler's welded on now. Couldn't I just weld the cut one as well?

[Tower]

Yes, sure.

[78CB750CAFE]

2 1/2 pipes into a 2 1/4  free flowing muffler is what I run and it runs and sounds great. I paid way too much to get a flange/adapter welded up at a local muffler joint, but there are easier answers if your muffler is a slip on, or has a collar for attachment. Most auto shops have cheap pre made reducers for exhaust pipes if your mufflers adapters dont work well.

Um...Yeah I'm pretty sure we are gonna need more pics please and a full report on that beast would render a big fat thankyou from the goon is that a two brothers racing pipe ya got there, what did the pipe spec out for originally.

I will get some detailed pics of the adapter/flange deally today, it should be easy since my pipe is off so I can replace my cracked oil pan. The pipe is a Two Bros Racing VALE2 carbon from a CBR600R a local guy built that was way beyond what he could handle... He put around $3K into hopping it up and within the first week looped it off a stoplight. He promptly sold the damaged bike back to my local dealer for nothing, and my buddy at the parts counter sold me the $600 carbon pipe for $50

Here is a detail page on the build: http://www.drewfusnation.com/cb750caferacer.htm

[goon 1492]

2 1/2 pipes into a 2 1/4  free flowing muffler is what I run and it runs and sounds great. I paid way too much to get a flange/adapter welded up at a local muffler joint, but there are easier answers if your muffler is a slip on, or has a collar for attachment. Most auto shops have cheap pre made reducers for exhaust pipes if your mufflers adapters dont work well.

Um...Yeah I'm pretty sure we are gonna need more pics please and a full report on that beast would render a big fat thankyou from the goon is that a two brothers racing pipe ya got there, what did the pipe spec out for originally.

I will get some detailed pics of the adapter/flange deally today, it should be easy since my pipe is off so I can replace my cracked oil pan. The pipe is a Two Bros Racing VALE2 carbon from a CBR600R a local guy built that was way beyond what he could handle... He put around $3K into hopping it up and within the first week looped it off a stoplight. He promptly sold the damaged bike back to my local dealer for nothing, and my buddy at the parts counter sold me the $600 carbon pipe for $50

Here is a detail page on the build: http://www.drewfusnation.com/cb750caferacer.htm

WOW! and thank you for the link, that thing is double sharp!